Thread-controlled contact device for power driven sewing machines



K. WINZ THREAD-CONTROLLED CONTACT DEVICE FOR POWER DRIVEN SEWINGMACHINES July 21, 1959 Filed March 13, 1957 United States PatentMEAD-CONTROLLED CONTACT DEVICE FOR POWER DRIVEN SEWING MACHINES KarlWinz, Kaiserslautern-Pfalz, Germany, assignor to G. M. Pfalr A.G.,Kaiserslautern-Pfalz, Germany, a corporation of Germany ApplicationMarch 13, 1957, Serial No. 645,691 Claims priority, application GermanyMarch 27, 1956 2 Claims. (Cl- 112-219) The present invention relates tothread-controlled electrical contact devices for power driven sewingmachines, more particularly to contact devices actuated by the upper orneedle thread on failure of the lower or bobbin thread, to effect thestoppage of the machine by disconnecting it from its power supply orde-clutching it'from its driving means, in an effort to avoid wastefulrunning and other defects.

A known arrangement of this type comprises an oscillating leverpivotally mounted upon a support secured to the presser foot bar of themachine. The lower end of the lever is bent at a right angle andextended to a point immediately behind the needle and transverse to thesewing direction. There is further secured to the lower end of saidlever a frame or loop engaged by the end of a contact bar. The latter ispivotally supported by a bearing mounted upon the cloth plate or tabletop of the machine and cooperates with a fixed insulatingly mountedcontact. Upon displacement of the needle thread due to failure orbreakage of the lower thread, the lever is deflected in the sewingdirection, whereby the contact arm being disengaged from said frame iscaused to fall and close the contacts of the device. This, in turn,closes a relay circuit or the like effecting the stoppage of themachine.

Devices of this type have the disadvantage that, due to the arrangementof the lever with its thread-actuated part transverse to the sewingdirection and above the presser foot, a substantial number of unbound oridle stitches are required, to cause a displacement of the upper threadsuflicient to effect closing of the contacts. Furthermore, the partsbeing mounted upon the table top obstruct or otherwise interfere withthe operation of the machine. For this reason, devices of this are onlysuitable practically for machines designed for edge seaming or bindingpurposes.

Other known contact devices of this type comprise a pivoted lever havinga movable contact and cooperating with fixed contact arm, both mountedupon the presser foot of the machine. The contacts are normally urged toopen position by a spring, the movable contact arm being arranged withits lower end extending to a point close to the needle thread above thepresser foot. There is further provided an electromagnet upon the fixedcontact arm becoming energized upon closing of the contact device andactuation of the stoppage means of the machine, to maintain the movablecontact arm in closed position until a main control switch of themachine is closed after removal of the disturbance or thread failure.

Again, with contact devices of this type, the lower end of the movablecontact arm controlled by the needle thread must be spaced by a certaindistance from the presser foot, thus requiring a substantial number ofunbound or idle stitches to initiate the closing of the contacts and, inturn, the stoppage of the machine. Furthermore, it is difiicult to mounta contact device of remaining parts or without interfering with theproper operation of the machine.

For practical purposes and in the interest of safety, not more thanabout two unbound stitches should occur. upon actuating of the contactdevice and prior to the stoppage of the machine, to prevent jammingthreads.

and other defects. This aim could not be achieved by the known devicesfor the reasons as pointed out and being obvious from the foregoing.

Accordingly, an object of the present invention is the' provision of asimple and improved thread-actuated contact device to effect theautomatic stoppage of a power driven sewing machine by which the aboveand related difiiculties and drawbacks are substantially overcome.

A more specific object of the invention is to provide a control deviceof this type which can be used in connection with any type of stitchingmaterial or sewing operation.

Still another object of the invention is the provision of athread-controlled contact device of the type referred to for powerdriven sewing machines which can be structurally embodied inconventional sewing machines without essential changes in the design andconstruction of the machines and without interfering with the normaloperation thereof.

Yet another object of the invention is the provision of a contact deviceactuated by the displacement of the upper or needle thread of aconventional sewing machine consequent on the breakage or failure of thelower or bobbin thread, whereby closing of the contacts of the device iseffected substantially instantly on thread failure, that is, with aminimum of the idle or unbound stitches being effected during theinterval between the thread failure and engagement of the contacts.

The invention, both as to its further objects as well as novel aspects,will be better understood from the following detailed description takenin reference to the accompanying drawing, forming part of thisspecification and showing a fractional perspective view of aconventional sewing machine embodying an improved contact deviceconstructed in accordance with the principles of the invention.

With the foregoing objects in view, the invention involves generally theprovision of an improved contact device of the type referred to suitablefor structural embodi ment with the presser foot base of a power drivensewing normally out of contact therewith.

The presser foot base is provided with a recess close to the needle,further means being provided to cause said thread-controlled portion orextension of said lever to resiliently engage the sewing material by theaction of a biasing spring normally urging the frame or lever in a thistype upon the presser foot without obstructing the Q downward direction.Upon failure or breakage of the lower or bobbin thread, the upper threadno longer emerges directly or straight from the stitching material closeto the needle, but assumes an oblique position or slack dragging andraising the contact frame and effecting engagement thereof with acooperating contact fixedly mounted upon said presser foot. As a result,a relay or the like connected in a circuit including the contact deviceinitiates the stoppage of the machine. Due to the provi sion of therecess in the presser foot base enabling the movable contact to beextended to a point close to the Patented July 21, 1959,

3 needle thread and into direct contact with the work or stitchingmaterial, actuation of the contact device is effected practicallyinstantly and involving a minimum number of idle or unbound stitches onthe failure or breakage of the lower thread. Furthermore, the contactdevice may be structurally embodied within the confines of the presserfoot base of conventional machines, substantially i.e. without anyprojecting parts or without requiring changes in the design thereof, aswill become further evident hereafter.

Referring more particularly to the drawing, the numeral 1 indicates thecloth plate of a conventional sewing machine connected with theoverhanging arm 2 by an upright or standard (not shown), said armterminating in a head 3 having mounted therein a reciprocating needlebar 5 carrying a needle 4 and presser foot bar 6, all of standardconstruction well known in the art. The lower end 7 of the presser footbar 6 is of square shape to receive the presser foot 8 removably securedthereto by means of a screw 9. The presser foot, in a known manner,resiliently engages the stitching plate 10 or sewing material,respectively, in the operative position, said plate being mounted flushwith the cloth plate 1 underneath which are arranged in known manner thecooperating stitch forming tools, such as the loop taker and feed dogmechanism, not shown in the drawing for simplicity and being unessentialfor the understanding of the invention.

The pressure foot, in the example shown, comprises a vertical shaft 11and a horizontal base 12 having a pair of bearings 13 and 14 supportinga shaft 15 pivotally connecting the base 12 with the shaft 11 of thepresser foot. The base 12 has an enlarged rear portion 16 provided witha bore 17, wherein is pivotally mounted the rear portion 18 of a contactframe or lever 19, portion 18 being surrounded by a spiral spring 20within said recess. The spring 20 has one end secured to the rearportion 16 of the base 12 and has its opposite looped-shaped end 22arranged to engage the intermediate portion 19 of the contact frame orlever, in such a manner that the front portion 23 of the frame will beresiliently urged in a downward direction upon the stitching plate 10 orthe work passed therebetween and the presser foot by the feed mechanismduring the operation of the machine.

For this purpose, the base 12 of the presser foot is provided with anoblong recess 24 close to the needle thread and at right angle tothe'stitching direction, said recess adapted to receive the front part23 of the contact frame 19. The latter thus extends to a pointimmediately adjac'ent to the point of emergance of the needle thread 31from the work or stitching material. As a result, the frame will bedeflected substantially instantly, that is, with a minimum number ofunbound stitches being eifected, upon failure or breakage of the lowerthread by the displacement or slack formed by the upper thread 31 beingdragged over the base of the foot in the rearward direction, in a mannerreadily understood.

The end 25 of the part 23 constituting a 'movable contact cooperateswith a fixed contact 26 insulatingly mounted upon the bearing 13 betweena-pair of insulating sheets or layers 27 and secured by means of a screw28 or in any other suitable manner. Contact 26 is connected to anelectrical conductor 29 which may, in turn, be connected to one pole ofa suitable current source through a relay or the like (not shown), theopposite pole of said source being connected to the metal parts of themachine to complete the electrical circuit of the contacts 25 and 2 6of; the device, in a manner readily understood.

The lower end of the shaft 11 of the presser foot 8 is shown providedwith a recess 30 to enable the upper thread 31 on failure of the lowerthread to readily form a slack or assume an oblique position to insuresafe and positive actuation of the contacts by the frame or lever 19 onthe occurrence of a lower thread failure.

In the drawing, the contact frame and needle thread are shown in theirposition during operation; or normal stitch formation of the machine. Inthis case, the frame has its front portion 23 resiliently engaging thework or stitching material with a light pressure, acting, so to speak,as a feeler or probe of the seam being stitched. Upon failure of thelower thread, the upper thread will be extracted from the work to forman oblique slack in the rearward direction of the presser foot. As aresult, the front portion 23 of the frame 19 being engaged by the threadis raised against the action of the spring 20 to effect closing of thecontacts 25 and 26 and, in turn, to initiate the stoppage of themachine. The machine may be stopped in any known manner, such as bydisconnecting it from its power supply or by de-clutching it from itsdriving means, or in any other suitable manner known in the art. At thesame time upon stopping of the machine, a warning signal may be producedindicating the thread failure.

In the foregoing the invention has been described with reference to aspecific illustrative device. It will be evident, however, thatvariations and modifications, as well as the substitution of equivalentelements for those shown for illustration, may be made without departingfrom the broader scope and spirit of the invention as set forth in theappended claims. The specification and drawing are accordingly to beregarded in an illustrative rather than in a restrictive sense.

1 A thread-controlled electrical contact device for lock-stitch sewingmachines having a needle and a presser foot comprised of a verticalshaft and a horizontal base connected thereto and engaging a work piecein the lowered position, said device comprising a lever having a rear;portion pivotally mounted upon the rear portion of said base. behindsaid shaft, as viewed in the sewing direction, and about an axistransverse thereto, said lever extending in a direction opposite to thesewing direction above and substantially parallel to said base andhaving a front portion at right angle to the sewing direction, saidfront portion forming a first contact element movable substantiallyvertically within a corresponding recess in the front portion of saidbase close to the path of said needle, spring biasing means for saidlever, to urge said contact element into continuous resilient engagementwith said work piece in the lowered position of said presser foot, and asecond, cooperating contact element mounted upon said base adjacent tosaid first contact element.

2. A thread-controlled electrical contact device for lock-stitch sewingmachines having a needle and a presser foot comprised of a verticalshaft and a horizontal base connected thereto and engaging a work piecein the lowered position, said device comprising a lever having a rearportion at right angle to the sewing direction and pivotally mountedabout its axis upon the rear portion of said base. behind said shaft, asviewed in the sewing direction, said lever extending in a directionopposite to the sewing direction laterally of said shaft andsubstantially parallel to said base and said lever having a frontportion at right angle thereto forming a first contact element,saidfront portion located and movable substantially vertically within arecess in the front portion of said base close to the path of saidneedle, a coiled spring to bias saidlever concentric to the rear portionthereof, to urge said contact element into continuous resilientengagement'with said work piece in the lowered position of said presserfoot, and a second cooperating contact element insulatingly mounteduponsaid base adjacent to said first contact element.

Vossen Oct. 30, 1945 Vossen May 22, 1956

